1 Corinthians 8:7

7 But not everyone possesses this knowledge. Some people are still so accustomed to idols that when they eat sacrificial food they think of it as having been sacrificed to a god, and since their conscience is weak, it is defiled.

Read 1 Corinthians 8:7 Using Other Translations

Howbeit there is not in every man that knowledge: for some with conscience of the idol unto this hour eat it as a thing offered unto an idol; and their conscience being weak is defiled.
However, not all possess this knowledge. But some, through former association with idols, eat food as really offered to an idol, and their conscience, being weak, is defiled.
However, not all believers know this. Some are accustomed to thinking of idols as being real, so when they eat food that has been offered to idols, they think of it as the worship of real gods, and their weak consciences are violated.